1. Field of the Invention
The present invention relates to an active mechanical support system which is useful in supporting a body by means of a plurality of support pads each of which is connected to an actuator which includes an actuator cylinder and an actuator rod. The support pads are connected to the actuator rod and displaced relative to the actuator cylinder to selectively raise and lower portions of the body in response to actuator displacement control signals and support pad body contact pressure signals.
2. Description of the Prior Art
Human patients who are at risk of developing pressure ulcers (bed sores) are currently placed on foam cushions, air cushions, low air loss beds or beds that have fluidized beads to provide low values of tissue interface pressure. Since tissue interface pressure is a major contributor to pressure ulcers, it is desirable to reduce forces at the surface of tissue to the lowest values possible in treating and preventing pressure ulcers. Each such prior art device reduces tissue interface pressure to varying degrees. However, foam products generally are not able to reduce tissue interface pressure below 32 mm Hg., the capillary closure pressure in humans, on prominent bony areas like the greater trochanter. Air cushion products can reduce interface pressure normal to the surface to values below 32 mm Hg. but under certain use conditions can develop higher interface pressures when surface material is under tension. This condition can be produced by shear forces or when material is stretched by the anatomy to form a hammock-like structure. Low air loss beds are prone to similar deviations from ideal performance. Beds with fluidized beads provide good flotation but it is difficult to support the whole patient on them without external props which in turn cause a loss of flotation effectiveness in places where props are used.
Various controlled cushion-type devices are known. For example, U.S. Pat. No. 4,864,671 to Evans relates to a controllably inflatable cushion including a plurality of independently inflatable rows or zones of cushions which are inflated/deflated by means of a pump and valves which are controlled by a microprocessor control means which receives input from a pressure sensor and input switches. The switches allow the user to set desired inflation sequences and the pressure sensor provides feedback signals to control inflation pressure. The cushions are formed of a plurality of cells which contract and expand in an accordian fashion.
U.S. Pat. No. 4,799,276 to Kadish relates to a body rest including a matrix of freely displaceable supports in the form of free floating, pressurized air-supported pistons which collectively form a couch surface of a bed. Pressure exerted by the patient against each respective piston is constantly measured. The pistons are periodically caused to move downward and then brought back to their initial high level. The pistons include a stem and a head portion. The stem reciprocates in response to hydraulic or pneumatic inflation or deflation of a sleeve as directed by a microprocessor. The head portions each constitute a fraction of a continuous couch surface of the body rest. Capacitive pressure sensors and a scanning system to monitor the pressure conditions prevailing with respect to each support member.
U.S. Pat. No. 3,551,924 to Frye relates to a variable firmness mattress which includes a plurality of vertically movable support rods. Means are provided to vertically vary upward bias of the rods. Each rod includes a flexible head element for universal tilting relative to the rod axis. FIG. 7 depicts the support structure as including a rod, head element with flanged area and a ball and socket arrangement.
U.S. Pat. No. 3,879,776 to Solen relates to a variable tension fluid mattress including a plurality of individual inflatable pads wherein the pressure in various zones can be varied by setting a pressure sensitive switch as desired. In this manner a motor and pump maintain pressure as desired.
U.S. Pat. No. 3,656,190 to Regan et al. describes a plurality of supports with mechanical control for a wave-like motion.
U.S. Pat. No. 4,890,235 to Reger et al. relates to a system for generating a prescription wheelchair or other seating or body arrangement which includes a deformable seat portion. A patient to be fitted is placed upon a seat and thereby generated in response to which the seat surface can be selectively varied by a plurality of pneumatic actuators to provide an updated force distribution signal. In this manner, a preselected force distribution of the patient on the seat is provided. Such data is transmitted to a fabrication unit to allow for fabrication of a permanent seat cushion. A related system is described at pages 234-235 of "RESNA 12th Annual Conference," New Orleans, La. (1989).
Notwithstanding the foregoing teachings, it is desirable to provide a mechanical flotation system which has the ability to reduce body tissue interface pressure normal to the body to its theoretical minimum limit. It is further desirable to provide a mechanical flotation system which relieves shear forces in the plane of the body tissue and support pad interface. It is also desirable to provide a mechanical flotation system which can apply message and wave motion in three dimensions to the patient for comfort enhancement. It is further desirable to provide a mechanical flotation system which is useful in positioning the elevation of the anatomy of the patient similar to gatching of the bed or raising of the head. It is also desirable to provide a mechanical flotation system which is useful in turning or rocking the patient around an axis which extends longitudinally relative to the patient. It is also desirable to provide a mechanical flotation system which facilitates momentarily reducing to zero local body tissue interface pressure in problem locations.
In addition to providing treatment for patients, it is desirable to provide a mechanical flotation system which can be used as a measuring instrument to determine various features of the human anatomy placed upon the supporting surface of the system. Such features include, without limitation, body contours, spring rate or compliance of tissue, extend of joint movement, resistance force of joint rotation, and surface temperature at each contact point. It is further desirable to provide a mechanical flotation system wherein such features can be completely mapped over the extent of the anatomy. It is also desirable to provide a mechanical flotation system useful in diagnostic work and patient condition analysis prior to treatment.
It is also an objective to provide a mechanical flotation system wherein the ratio of a change of force on body tissue to a change of body tissue displacement produces a measure of body tissue stiffness. It is another objective to provide a mechanical flotation system wherein the spring rate of a patient support surface can be adjusted and controlled by varying the ratio of body contact pressure to displacement of body tissue.